This invention relates to a laser device having an infrared laser medium and an aperture member disposed within the resonator.
FIG. 1 shows schematically, in cross section, a typical example of a conventional laser device of this type. In FIG. 1, an a.c. high voltage source 1 is connected between a pair of facing electrodes 2 and 3. A silent discharge 4 can be established in a space between the electrodes 2 and 3. A partial reflecting mirror 5 is disposed at one end of the space and a total reflecting mirror 6 is disposed at the other end of the space. An aperture member 7 is disposed between the partial reflecting mirror 5 and the other end of the space to suppress all laser modes other than a principal beam. The provision of each aperture member is disclosed in U.S. Pat. No. 3,904,983. In the space formed between the electrodes 2 and 3, a laser gas medium flows orthogonally of a plane of the sheet as shown by reference numeral 8. A thick arrow 9 indicates an output laser beam.
In operation, a high a.c. voltage is applied by the power source 1 across the space between the electrodes 2 and 3 to establish a silent discharge 4. At the same time, the laser gas medium flows as mentioned. The laser gas medium is excited by the silent discharge 4 to produce a laser light. A portion of the laser light directed to the mirror 6 is reflected back to the aperture member 7 and collimated thereby. A portion of the laser light directed to the half-silvered mirror 5 is partially reflected. Thus the laser beam 9 having a cross-sectional shape corresponding to an aperture 7a of the aperture member 7 is obtained. In this case, the relative position of the partial reflecting mirror 5 to the mirror 6 must be well aligned, otherwise, the mode symmetry of the laser beam 9 is broken.
Furthermore, the mode symmetry of the laser beam should be detected. However, there have been no such detection means provided in the conventional laser apparatus and thus it has been very difficult to obtain a laser beam whose mode symmetry is excellent.
U.S. Pat. No. 4,391,519 discloses an axis monitoring system for laser beams in which an externally produced ring-shaped light is introduced into a laser oscillator and reflected back. Mirrors of the laser are adjusted such that an axis of the reflected ring-shaped light and an axis of a laser output beam coincide with each other.
U.S. Pat. No. 4,393,303 discloses a deformable mirror which is controlled by a power meter and a phase control power meter such that inputs of these power meters are maximized.
These prior art devices utilize various complicated means disposed externally of the laser resonator, making the device bulky and expensive.
Further, in these prior art arrangements, the alignment of the optical axis of the resonator with the axis of the laser beam is obtained not by optimizing the laser beam symmetry but by maximizing the input to the laser beam detectors disposed externally of the resonator.